Multi-element thermocouple

ABSTRACT

A multi-element thermocouple circuit includes at least two temperature measuring junctions. A first temperature measuring junction is formed by first and second thermoelements, each of the first and second thermoelements being formed of a noble metal or a noble metal alloy. The second temperature measuring junction, which connects to the distal end of the first thermoelement, is formed by third and fourth thermoelements, neither of which is formed from a noble metal or a noble alloy. A fifth thermoelement connects to the distal end of the second thermoelement and is formed of the same material as the fourth thermoelement. During operation, the distal ends of the third and fourth thermoelements define therebetween a first voltage difference corresponding to a temperature at the second temperature measuring junction, while the distal ends of the fourth and fifth thermoelements define a second voltage difference from which a temperature at the first temperature measuring junction may be obtained.

RELATED APPLICATIONS

The present invention is a Continuation of U.S. patent application Ser.No. 10/851,248, filed, May 24, 2004, now U.S. Pat. No. 7,044,638. Thecontents of aforementioned U.S. patent application Ser. No. 10/851,248are incorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention is directed to thermocouples. More particularly,it is directed to multi-element thermocouple circuits and correspondingthermocouple assemblies capable of measuring high temperatures

BACKGROUND INFORMATION

Noble metal thermocouples, such as Type-R (Pt-13% Rh vs. Pt) and Type-S(Pt-10% Rh vs. Pt) thermocouples, among others, may be used formeasuring hot gas temperatures in excess of 1300° C. For turbineapplications, thermocouple probes typically are on the order of 10 cm–30cm in length. Noble metal extension wires, thermoelectrically matched orcompensating type to the thermoelements of such a thermocouple, may beused to bridge a distance between a distal end of the thermocouple andelectrical circuitry configured to receive and process its output. Thecircuit extension may also include terminal connections to facilitateprobe installation and maintenance.

Under certain conditions, it may become necessary to have very longextension wires. This may happen, for example, where the geometry andphysical constraints of the object producing the hot gases to bemeasured, and the location within the object where these hot gases areaccessible, are such that the electrical circuitry cannot be placednearby. For noble metal thermocouples, the extension wires and terminalcomponents may not be commercially available or cost prohibitive for therequired length.

SUMMARY OF THE INVENTION

In one aspect, the present invention is directed to a multi-elementthermocouple circuit. The circuit includes a first thermocouplecomprising first and second thermoelements meeting at a firsttemperature measuring junction and having respective first and seconddistal ends, the first and second thermoelements being formed ofrespective first and second materials. It also includes a secondthermocouple comprising third and fourth thermoelements meeting at asecond temperature measuring junction that is connected to the firstdistal end, the third and fourth thermoelements having respective thirdand fourth distal ends and being formed of respective third and fourthmaterials, neither of said third and fourth materials being the same aseither the first or second material. The circuit also includes a fifththermoelement having a fifth proximal end connected to said seconddistal end and a fifth distal end, the fifth thermoelement being formedof a same material as the fourth thermoelement.

In one embodiment, each of the first and second thermoelements comprisesa noble metal or a noble-metal alloy.

In another aspect, the present invention is directed to a parallelthermocouple circuit having a plurality of identical multi-elementthermocouples as described above. In the parallel thermocouple circuit,the third thermoelements of all the multi-element circuits are connectedto a first electrical terminal, the fourth thermoelements of all themulti-element circuits are connected to a second electrical terminal,and the fifth thermoelements of all the multi-element circuits areconnected to a third electrical terminal.

In yet another aspect, the present invention is directed to athermocouple probe. The probe includes a first thermocouple comprisingfirst and second thermoelements meeting at a first temperature measuringjunction, the first and second thermoelements being formed of respectivefirst and second materials. The probe also includes a secondthermocouple comprising third and fourth thermoelements meeting at asecond temperature measuring junction that is connected to the firstthermoelement, the third and fourth thermoelements being formed ofrespective third and fourth materials, neither of said third and fourthmaterials being the same as either said first or second material. Theprobe also includes a fifth thermoelement connected to the secondthermoelement and being formed of the fourth material.

In yet another aspect, the present invention is directed to athermocouple assembly comprising the above-described thermocouple probedetachably connected to a multi-conductor cable.

In still another aspect, the present invention is directed to a methodfor determining a temperature T2 of a turbine engine gas stream. Themethod includes exposing a first thermocouple to the turbine gas stream;exposing a second thermocouple to a transitional temperature T1 whileshielding the second thermocouple from said turbine gas stream,detecting a first voltage difference associated with the firstthermocouple, detecting a second voltage difference associated with thesecond thermocouple, estimating a transitional temperature T1 based onthe first voltage difference, and estimating the turbine gas streamtemperature T2 based at least in part on an estimated value of thetransitional temperature T1 and the second voltage difference.

In yet another aspect, the present invention is directed to a method ofcontrolling a turbine engine based on the estimated gas streamtemperature T2.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows one embodiment of a multi-element thermocouple circuit inaccordance with the present invention.

FIG. 2 shows a second embodiment of a multi-element thermocouple circuitin accordance with the present invention.

FIG. 3 shows a parallel thermocouple circuit in accordance with thepresent invention.

FIG. 4 a shows a perspective view of a mating assembly in accordancewith the present invention.

FIG. 4 b shows a partial cross-sectional view of a thermocouple probe inaccordance with the present invention.

FIGS. 5 a–5 d shows cross-sectional views of various mating assemblyembodiments.

FIG. 6 shows a thermocouple assembly in accordance with the presentinvention configured to measure gases in a turbine engine.

FIG. 7 shows a control system employing a thermocouple assembly inaccordance with the present invention.

DETAILED DESCRIPTION

FIG. 1 shows a multi-element thermocouple circuit 100 in accordance withthe present invention. The thermocouple circuit 100 corresponds to athermocouple assembly comprising two thermocouples 102, 112 with sharedcomponents.

The thermocouple circuit 100 includes a primary thermocouple 102comprising a first thermoelement 104A and a second thermoelement 104B.Preferably, the first and second thermoelements each are a noble metalor a noble alloy. For example, the first thermoelement 104A (positive)may be a platinum-rhodium alloy and the second thermoelement 104B(negative) may be platinum.

In one embodiment the first and second thermoelements are part of anoff-the-shelf Type-R thermocouple probe. In an alternate embodiment, thefirst and second thermoelements belong to a non-letter designatedthermocouple. An example of this may be to have the first thermoelementformed of platinum and the second formed of palladium. In yet anotherembodiment, the first and second thermoelements are deposited on, andsupported by, a thermally conductive and electrically non-conductivesubstrate. Regardless of how they are implemented, the first and secondthermoelements preferably are less than 30 cm long and more preferablyare less than 20 cm long.

The first and second thermoelements 104A, 104B, at respective proximalends 106A, 106B thereof, meet at a first temperature measuring junction108. During use, the temperature to be determined may be some very high,unknown temperature T2. Distal ends 110A, 110B of the first and secondthermoelements 104A, 104B, respectively, are spaced apart from oneanother, and both preferably are at a same transition temperature T1.

The thermocouple circuit 100 also includes an auxiliary thermocouple 112comprising a third thermoelement 114C and a fourth thermoelement 114D.Thus, it is noted that neither the third nor fourth thermoelements 114C,114D is formed of the same material as the first thermoelement 104A.Preferably, too, neither the third nor fourth thermoelement is formed ofthe same material as the second thermoelement 104B. In a preferredembodiment the third and fourth thermoelements are part of a base metaltype (e.g., Type-K or Type-T) thermocouple. Thus, the thirdthermoelement 114C (positive) may be KP material and the fourththermoelement 114D (negative) may be KN material, in a Type-Kimplementation.

The thermoelements 114C, 114D, at respective proximal ends 116C, 116Dthereof, meet at a second temperature measuring junction 120 where thetemperature may be at the previously mentioned transition temperatureT1. Distal ends 118C, 118D of the third and fourth thermoelements 114C,114D, respectively, connect to first and second electrical terminals128A, 128B, respectively. The electrical terminals 128A, 128B are spacedapart from one another and both preferably are at some known referencetemperature T0.

During operation, the electrical terminals 128A, 128B define betweenthem a first voltage difference E1 that is reflective of the temperaturedifference T1−T0. Therefore, the auxiliary thermocouple 112 isconfigured to provide information for determining the transitiontemperature T1, given the reference temperature T0 from:E1=S _(CD)(T1−T0); or  (Eq. 1)

$\begin{matrix}{{T1} = {{T0} + \frac{E1}{S_{CD}}}} & \left( {{Eq}.\mspace{14mu} 2} \right)\end{matrix}$

where S_(CD) is the mean relative Seebeck coefficient of materials ‘C’and ‘D’ between temperatures T0 and T1, which in this instancecorrespond to the third 114C and fourth 144D thermoelements,respectively.

The thermocouple circuit 100 also includes a fifth thermoelement 122Dthat has the same length as, and is formed of the same material as, thefourth thermoelement 114D. Thus, fifth thermoelement 122D is formed of amaterial that is different from second thermoelement 104B. Fifththermoelement 122D has a proximal end 124B that is connected to thesecond thermoelement 104B at junction 130, and a distal end 126D that isconnected to a third electrical terminal 128C.

During operation, the second electrical terminal 128B and the thirdelectrical terminal 128C define between them a second voltage differenceE2 that is reflective of the temperature difference T2−T1. Therefore,the primary thermocouple 102 is configured to provide information thathelps determine the unknown temperature T2 according to the following:E2=S _(AB)(T2−T1)+S _(DD)(T1−T0);  (Eq. 3)

-   -   and if S_(DD)=0; then        E2=S _(AB)(T2−T1), and  (Eq. 4)

$\begin{matrix}{{T2} = {{T1} + \frac{E2}{S_{AB}}}} & \left( {{Eq}.\mspace{14mu} 5} \right)\end{matrix}$

where S_(AB) is the mean relative Seebeck coefficient of materials ‘A’and ‘B’ between temperatures T1 and T2, which in this instancecorrespond to the first 104A and second 104B thermoelements,respectively, and S_(DD) is the mean relative Seebeck coefficient toaccount for the fourth 114D and fifth 122D thermoelements, respectively.However, the fourth 114D and fifth 122D thermoelements, whicheffectively serve as extension wires, do not need to bethermoelectrically matched with primary thermocouple 102 provided thatthey both are of identical composition, thereby justifying theassumption that S_(DD) is indeed zero.

In actual practice, the calculation is more complicated than describedsince the relative Seebeck coefficient is a function of temperature.However, constructing a thermocouple assembly with standard thermocouplematerials, such as described in ASTM E230, allows one to use industryaccepted E(T) equations and related tolerances. An example output usinga Type R (Pt-13Rh vs. Pt) hot section thermocouple and Type-K extensionis shown in Table 1 below.

TABLE 1 Nominal output for Type R thermocouple with Type K ExtensionT0(° C.) T1(° C.) T2(° C.) E1(mV) E2(mV) 20 150 900 5.340 8.164 10009.465 1100 10.809 1200 12.187 1300 13.588 200 900 7.340 7.736 1000 9.0371100 10.381 1200 11.759 1300 13.160 250 900 9.355 7.282 1000 8.583 11009.927 1200 11.305 1300 12.706

Thus, upon detecting the voltages E1 and E2, one may use establishedequations and/or tables such as this one, to calculate and/orinterpolate, as needed, to estimate the temperatures T1 and T2.

As seen in the circuit of FIG. 1, the third 114C and fourth 114Dthermoelements belong to a first voltage difference subcircuit whichproduces the first voltage difference E1; the first 104A, second 104B,fourth 114D and fifth 122D thermoelements belong to a second voltagedifference subcircuit which produces the second voltage difference E2.The distal ends of the third 114C, fourth 114D and fifth 122Dthermoelements are sufficiently electrically isolated from one anotherto allow measurement of the first open circuit voltage difference E1between the third 114C and fourth 114D thermoelements and allowmeasurement of the second open circuit voltage difference E2 between thefourth 114D and fifth 122D thermoelements. Significantly, the fourth114D thermoelement is common to the two voltage difference subcircuits.The third 114C, fourth 114D and fifth 122D thermoelements preferablycomprise conductors, such as 20 AWG wire, individually insulated andbundled together as a multi-wire flexible cable 140 extending betweentheir proximal and distal ends. And since the fourth and fifththermoelements preferably are formed of the same material, themulti-wire cable has first and second identical conductors, and a thirdconductor formed of a different material that is suitable for forming athermocouple (e.g., Type-K or type-T) with one of the two identicalconductors.

The length of third 114C, fourth 114D and fifth 122D thermoelements,which effectively serve as extension wires, preferably is anywhere fromless than 20 cm to several meters. The resulting thermocouple assemblythus is suitable for measuring a high, unknown temperature T2 by makingtwo voltage measurements, using a primary thermocouple 102 that iscascaded, via its first thermoelement 104A, with an auxiliarythermocouple 112 configured to measure a transition temperature T1.

The thermocouple assembly may thus be used to measure temperatures withthe primary thermocouple 102 proximate to the hostile environment, andthe auxiliary thermocouple extending from a leg of the primarythermocouple to a remote location where the electrical connectors 128A,128B & 128C are situated. This allows one to use readily available basemetal extension wires and connectors, which provides cost advantageswhen using a noble metal primary thermocouple. Such base metal extensionalso allows one to use non-letter designated noble metal primarythermocouples in situations where matched lead wires and connectors arenot available.

In a preferred embodiment, the second temperature measuring junction 120and junction 130, where the second 104B and fifth 122D thermoelementsmeet, preferably are both at the same transition temperature T1. In oneembodiment, the junctions 120, 130 simply may be positioned close to oneanother to help ensure that they experience the same transitiontemperature T1. In another embodiment, in addition to simply beingproximate to one another, a mating assembly 132 is provided thatsupports portions of one or more of the first through fifththermoelements. More preferably, the mating assembly is such that thetwo junctions 120, 130 are electrically isolated from one another, yetare still in thermal communication with each other so that they canexperience a common temperature T1.

The electrical terminals 128A, 128B & 128C, at which the distal ends ofthe third 114C, fourth 114D and fifth 122D thermoelements terminate,preferably are all at a same, known, reference temperature T0. In oneembodiment, the electrical terminals are mounted on a termination strip134. The temperature of the termination strip 134 may be temperaturecontrolled to maintain the termination strip at a predeterminedreference temperature T0. Alternatively, or in addition, an auxiliarythermometer may be used to gauge the temperature at the terminals, andthe output of this thermometer is used as the reference temperature T0in the equations above to determine the temperature T2 at the firsttemperature measuring junction 108.

During use, the electrical terminals 128A, 128B & 128C provide thevoltage differences E1 & E2 to additional electrical circuitry, known tothose skilled in the art. This additional circuitry may, among otherthings, sense the voltage difference and convert it into analog and/ordigital signals, at least one of which preferably carries informationthat is proportional to temperature T2 for further processing. Thus, aprocessor associated with this circuitry may be configured to use one E1to determine the transition temperature T1 and, from that, thetemperature T2. The temperature T2, which is then determined as afunction of time, may then be used to provide real-time control of theequipment creating that temperature.

FIG. 2 shows an alternate embodiment of a multi-element thermocouplecircuit 200 in accordance with the present invention. The principaldifference between thermocouple circuit 100 and thermocouple circuit 200is that the latter is provided with identical, first and secondauxiliary thermocouples 212A, 212B, respectively, configured to measuretemperature T1 at respective second 220 and third 230 temperaturemeasuring junctions associated with mating assembly 232. Thus,multi-element thermocouple circuit 200 comprises a primary thermocouple202 to whose first and second thermoelements 204A, 204B, respectively,the first 212A and second 212B auxiliary thermocouples are connected ina cascaded fashion.

As seen in FIG. 2, primary thermocouple comprises first thermoelement204A formed from a first material, and second thermoelement 204B formedfrom a second material. Furthermore, first auxiliary thermocouple 212Acomprises third thermoelement 214C and fourth thermoelement 214D, whilesecond auxiliary thermocouple 212B comprises fifth thermoelement 222Dand sixth thermoelement 222C which meet at third temperature measuringjunction 230. It is understood that the third and sixth thermoelements214C, 222C are both formed of a third material and have the same length,while fourth and firth thermoelements 214D, 222D are both formed of afourth material and also have the same length.

In a preferred embodiment, thermoelements 214C, 214D, 222C & 222D allcomprise conductors bundled together in a multi-wire cable 240 extendingbetween their proximal and distal ends. And since the third 214C andsixth 222C thermoelements are formed of the same, third material whilefourth 214D and fifth 222D thermoelements are formed of the same, fourthmaterial, the cable 140 has two pairs of identical conductors formed ofmaterial suitable for implementing a pair of identical thermocouples(e.g., Type-K or Type-T). The distal ends of thermoelements 214C, 214D,222D & 222C connect to electrical terminals 228A, 228B, 228C & 228D,respectively, which are associated with termination strip 234.

During use, the first auxiliary thermocouple 212A outputs a voltagedifference E1 that is reflective of temperature T1, while the secondauxiliary thermocouple 212B outputs a voltage difference E3 that is alsoreflective of temperature T1. The two values E1 and E3 may both be usedto provide redundant T1 estimates. Alternatively, the individualjunction temperatures may be used to calculate T2 using absolute Seebeckcoefficients for thermoelements 204A, 204B, 214D and 222D.

FIG. 3 shows a parallel thermocouple circuit 300 that is configured todetect the temperature at a plurality of locations. Such an arrangementcan be especially advantageous when one wishes to measure thetemperature at a plurality of locations, all associated with the sameheat source. An example of this may arise in turbine application whereone may wish to mount temperature probes circumferentially around a hotsection of an engine.

The parallel thermocouple circuit 300 has a plurality of identicalmulti-element thermocouple circuits 302A, 302B, 302C arranged inelectrical parallel with one another, each being in accordance with themulti-element thermocouple circuit 100 of FIG. 1. As seen in FIG. 3, theparallel thermocouple circuit 300 has three first temperature measuringjunctions 308A, 308B, 308C formed by the juncture of three firstthermoelements 304A with three second thermoelements 304B, for measuringtemperatures T2, T2′, T2″, respectively.

The parallel thermocouple circuit 300 also has three second temperaturemeasuring junctions 310A, 310B, 310C, for measuring transitiontemperatures T1, T1′, T1″, respectively. All of the third thermoelements314C connect to first electrical terminal 328A; all of the fourththermoelements 314D connect to the second electrical terminal 328B; andall of the fifth thermoelements 322D connect to the third electricalterminal 328C.

During operation, the voltage difference E1 between first 328A andsecond 328B electrical terminals is reflective of an average oftemperatures T1, T1′, T1″. Similarly, voltage difference E2 betweensecond 328B and third 328C electrical terminals is reflective of anaverage of temperatures T2, T2′, T2″. For E1 and E2 to reflect theaverage temperatures, however, the loop resistance paths for theparallel circuits should be equal, and so the various thermoelementsshould be replicated in each of the multi-element thermocouple circuits302A, 302B, 302C.

It is understood that the parallel thermocouple circuit 300 correspondsto a thermocouple assembly comprising three multi-element thermocouplesthat share electrical terminals 328A, 328B and 328C. It is furtherunderstood that while FIG. 3 shows a multi-thermocouple circuit havingthree multi-element thermocouples, a different number, such as 2, 4, 5,etc., of multi-element thermocouples may likewise be connected inparallel.

FIG. 4 a shows a perspective, stylized view of a mating assembly 400 inaccordance with the present invention. It is understood that the matingassembly 400 may be part of a thermocouple probe assembly, being fixedto such a thermocouple's distal end, as seen in FIG. 4 b. The matingassembly may even have an exterior that is formed of the same materialas the outer sheath of the thermocouple, and manufactured continuouslytherewith. The mating assembly 400 preferably has a hollow metalliccylindrical body 412, receives first 404A and second 404Bthermoelements, and has third 414C, fourth 414D and fifth 422Dthermoelements emerging therefrom. A material 404 into which at leastportions of some of the thermoelements extend, is present in thecylindrical body. The second temperature measuring junction 420 wherethe third 414C and fourth 414D thermoelements join, and a junction 430where the second 404B and fifth 422D thermoelements meet are alsoassociated with the mating assembly.

FIG. 4 b shows a thermocouple probe 450 in accordance with an embodimentof the present invention. The primary thermocouple 412 has an outercylindrical sheath 440 and an end closure 442 formed of the samematerial at the proximal end of the probe 450. Within the cylindricalsheath 440 are the first thermoelement 404A and the second thermoelement440B, each of which preferably also is formed of a noble metal or noblemetal alloy, as discussed above. The sheath 440 and end closure 442preferably are formed of materials very similar to the thermoelementsthey enclosed. Thus, if the first thermoelement 404A is aplatinum-rhodium alloy and the second thermoelement is platinum, thesheath and end cap may, for instance, be formed of a platinum alloy.Preferably, the sheath and end cap are oxide-dispersion strengthenedwith zirconium oxide or yttrium oxide, or the like, to prevent largegrains from forming therein under the stress of high temperature.

The first and second thermoelements 404A, 404B, which meet at the firsttemperature measuring junction 408 proximate to the end closure 442, areembedded in an electrically non-conductive and thermally insulativematerial 444 such as high purity magnesium oxide or aluminum oxide. Theinsulative material 444 should be non-reactive at the high temperaturesto which the probe 450 would likely be exposed, thereby avoidingcontamination within the probe. A base cap 446 is provided with openings448 through which distal portions of the first and second thermoelements404A, 404B exit into the mating assembly 400. The mating assembly 400may be implemented in a one of a number of ways, as discussed next, suchthat third, fourth and fifth thermoelements 414C, 414D, 422D emergetherefrom.

FIG. 5 a shows a vertical cross-section of one embodiment of a matingassembly 520. Mating assembly 520 has a disc-shaped plug 524 positionedin the hollow cavity 526 defined by the cylindrical wall 502 of theassembly. The plug is preferably a ceramic or glass material with highresistivity for electrical isolation and high thermal conductivity topromote temperature uniformity within the mating assembly. Three holes528 are formed in the plug 524 to accommodate pins 530A, 530B, 530C. Thepins 530A, 530B, 530C are detachably connected to sockets 532A, 532B,respectively. Second temperature measuring junction 534, and junction536 where second thermoelement 504B and fifth thermoelement 522D meet,are both on the upstream side 538 of the mating assembly 520, and sothese junctions would be inside a probe. It is therefore understood thatpin 530A and socket 532A preferably are formed of the same material asthird thermoelement 514C, while pins 530B & 530C and sockets 532B & 532Cpreferably are all formed of the same material as the fourth 514D andfifth 522D thermoelements.

FIG. 5 b shows a vertical cross-section of a second embodiment of amating assembly 540. Mating assembly 540 also has a disc-shaped plug 524of the sort seen in mating assembly 520 discussed above. Two holes 548are formed in the plug 524 to accommodate pins 550A, 550B. The pins550A, 550B are detachably connected to sockets 532A, 532B, 532C,respectively. Second temperature measuring junction 554, and junction556 where second thermoelement 504B and fifth thermoelement 522D meet,are both on the downstream side 558 of the mating assembly 540 as sothese junctions would be outside a probe. It is therefore understoodthat pin 550A and socket 552A preferably are formed of the same materialas the first thermoelement 504A, while pin 550B and socket 552Bpreferably are all formed of the same material as the secondthermoelement 504B.

FIG. 5 c shows a vertical cross-section of a mating assembly 560 havinga solid core 562 formed from an electrically insulating pottingmaterial, such as a high-temperature cement. The temperature measuringjunction 564 is embedded within this core, as is a second junction 566where the second 504B and the fifth 522D thermoelements meet. In thisembodiment, a downstream portion of each of thermoelements 514C, 514Dand 522D is permanently fixed to the core 562, the three downstreamportions terminating, at a free end thereof, in a pigtail assembly 568.As is known to those skilled in the art, the pigtail assembly 568 mayconnect to another cable, much as seen in mating assembly 580 describedbelow. It is understood that such a cable, and any connectors betweenthe pigtail assembly and the cable, are formed of the same material asthe thermoelements to which they connect.

FIG. 5 d shows a vertical cross-section of yet another mating assembly580, again having a solid core 582 formed from a electrically insulatingpotting material, such as a high-temperature cement. The temperaturemeasuring junction 584 is embedded within this core, as is a secondjunction 586 where the second 504B and the fifth 522D thermoelementsmeet. In this embodiment, the downstream end 588 of the mating assembly580 is provided with a connector assembly 590 comprising firstconnectors 592A, 592B, 592C at which the third 514C, fourth 514D andfifth 522D thermal elements respectively terminate. First connectors592A, 592B and 592C are configured and dimensioned to mate withcomplementary second connectors 594A, 594B and 594C, respectively, whichare part of cable 596, to thereby continue the third 514C, fourth 514Dand fifth 522D thermal elements. It is understood that the connectorsare formed of the same material as the thermoelements to which theyconnect.

FIG. 6 shows a partial cross-section of a gas turbine engine 600 havinga thermocouple probe 602 in accordance with the present invention atleast partially installed in a tubular housing 604. The turbine engine600 has an outer fan region 610, an inner fan region 612 and an exhaustregion 614 that is at some time-varying temperature T2. A stator vane616 that extends into the gas path 614 is provided with an airflow hole618 that is in communication with the hot gas. The probe 602 is providedwith a mating assembly 626 and has a tip 606 that extends into theairflow hole 618.

The distal end 622 of the probe 602 extends into the bay 624 or othergeneral area in which the turbine engine 600 is situated. A matingassembly 626 connected to the probe 602 is located in the bay 624 and isexposed to the transitional temperature T1 of the bay 624, but isshielded from the hot turbine gas by the various turbine structures. Aflexible cable 628 then connects the mating assembly 626 to thenecessary electrical circuitry for detecting the voltages anddetermining temperature T1 and T2.

Thus, in accordance with the present invention, a method for determininga temperature T2 of turbine engine gas includes exposing a firstthermocouple to the turbine gas; exposing a second thermocouple to atransitional temperature T1 while shielding the second thermocouple fromsaid turbine gas, detecting first and second voltage differencesassociated with corresponding first and second thermocouples, estimatinga transitional temperature T1 based on the first voltage difference, andestimating the turbine gas temperature T2 based at least in part on anestimated value of the transitional temperature T1 and the secondvoltage difference, wherein the first and second thermocouples are ofdifferent types.

Another method for determining a temperature T2 of turbine engine gasincludes exposing a first thermocouple to the turbine gas; exposing asecond thermocouple to a transitional temperature T1 while shielding thesecond thermocouple from said turbine gas, detecting first and secondvoltage differences associated with corresponding first and secondthermocouples, estimating a transitional temperature T1 based on thefirst voltage difference, and estimating the turbine gas temperature T2based at least in part on an estimated value of the transitionaltemperature T1 and the second voltage difference, wherein at least aportion of an extension wire of a thermoelement of the firstthermocouple also serves as a thermoelement of the second thermocouple.

FIG. 7 shows a feedback loop 700 that controls operation of a turbineengine 702 using a thermocouple probe 704 in accordance with the presentinvention. Thermocouple probe 704 may be a probe such as that seen inFIG. 4 b, equipped with one of the mating assemblies of FIGS. 5 a–5 d. Acable 706 in which the third, fourth and firth thermoelements arebundled connects the distal end of the probe 70 to a signal conditioningunit 708.

The signal conditioning unit 708 detects the voltages E1 & E2, estimatesa temperature T2 of the turbine gas associated with the turbine engine702, and outputs a signal 710 that preferably is proportional to thisgas temperature. Thus, the signal conditioning unit 708 includescircuitry for detecting the voltages and converting them as appropriateinto analog or digital form, and a processor configured to accept theanalog or digital form of this voltage information and estimate thetemperature T2, in a manner discussed above. Thus, the processor of thesignal conditioning unit has one or more associated memories for storingdata of the sort seen in Table 1 along with software to interpolatevalues, and/or software to implement any necessary calculations toarrive at the required estimates.

The signal 710 output by the signal conditioning unit 708 is thenapplied as input to an engine controller 712 which compares theestimated temperature T2 with reference values and, as needed, outputs afeedback signal 714 that adjusts operation of the turbine engine 702.Thus, the feedback signal 714 may be used to control one or more valves,solenoids, actuators, motors, or the like, to adjust fuel intake, airintake, or other physical parameters, depending on the turbine enginedesign. It is understood that the signal conditioning unit 708 and theengine controller 712 may be integrated into a single device 720 thatperforms both functions.

Several embodiments of the present invention are specificallyillustrated and/or described herein. However, it will be appreciatedthat modifications and variations of the present invention are coveredby the above teachings and within the purview of the appended claimswithout departing from the spirit and intended scope of the invention.

1. A multi-element thermocouple circuit comprising: a first thermocouplecomprising first and second thermoelements meeting at a firsttemperature measuring junction and having respective first and seconddistal ends, said first and second thermoelements being formed ofrespective first and second materials; a second thermocouple comprisingthird and fourth thermoelements meeting at a second temperaturemeasuring junction that is connected to said first distal end, saidthird and fourth thermoelements having respective third and fourthdistal ends and being formed of respective third and fourth materials,neither of said third and fourth materials being the same as said firstmaterial; and a fifth thermoelement having a fifth proximal endconnected to said second distal end and a fifth distal end, the fifththermoelement being formed of said fourth material; wherein: the fourththermoelement is common to two voltage difference subcircuits; and thedistal ends of the third, fourth and fifth thermoelements are connectedto first, second and third electrical terminals, respectively, such thata first voltage difference is defined between the first and secondelectrical terminals, and a second voltage difference is defined betweenthe second and third electrical terminals.
 2. The multi-elementthermocouple circuit according to claim 1, wherein neither of the thirdand fourth materials is the same as the second material.
 3. Themulti-element thermocouple circuit according to claim 1, wherein thefifth thermoelement is the same length as the fourth thermoelement. 4.The multi-element thermocouple circuit according to claim 1, wherein:the first thermocouple is a type-R thermocouple; and the secondthermocouple is a type-K or a type-T thermocouple.
 5. The multi-elementthermocouple circuit according to claim 1, wherein: the firsttemperature measuring junction is at some temperature T2; the secondtemperature measuring junction is at some temperature T1; the third,fourth and fifth distal ends are at some known reference temperature T0;the third and fourth distal ends have a first voltage difference of E1between them; the fourth and fifth distal ends have a second voltagedifference of E2 between them; and the temperature T2 at the firstmeasuring junction can be estimated from E1 and E2.
 6. The multi-elementthermocouple circuit according to claim 1, further comprising a matingassembly having a first mating junction for connecting the first distalend to the second temperature measuring junction and a second matingjunction for connecting the second distal end to the fifth proximal end.7. The multi-element thermocouple circuit according to claim 6, whereinthe mating assembly is configured to electrically isolate the firstmating junction from the second mating junction and promote thermalconduction between the first and second mating junctions.
 8. Themulti-element thermocouple circuit according to claim 1, comprising amulti-wire cable that includes at least portions of the third, fourthand fifth thermoelements.
 9. The multi-element thermocouple circuitaccording to claim 1, further comprising a sixth thermoelement formed ofsaid third material, said sixth thermoelement and said fifththermoelement meeting at a third temperature measuring junction tothereby form a third thermocouple.
 10. A parallel thermocouple circuitcomprising a plurality of identical multi-element thermocouple circuits,each of said multi-element thermocouple circuits comprising: a firstthermocouple comprising first and second thermoelements meeting at afirst temperature measuring junction and having respective first andsecond distal ends, said first and second thermoelements being formed ofrespective first and second materials; a second thermocouple comprisingthird and fourth thermoelements meeting at a second temperaturemeasuring junction that is connected to said first distal end, saidthird and fourth thermoelements having respective third and fourthdistal ends and being formed of respective third and fourth materials,neither of said third and fourth materials being the same as said firstmaterial; and a fifth thermoelement having a fifth proximal endconnected to said second distal end and a fifth distal end, the fifththermoelement being formed of said fourth material; wherein: the thirdthermoelements of all of said plurality of identical multi-elementcircuits are connected to a first electrical terminal; the fourththermoelements of all of said plurality of identical multi-elementcircuits are connected to a second electrical terminal; and the fifththermoelements of all of said plurality of identical multi-elementcircuits are connected to a third electrical terminal.
 11. The parallelthermocouple circuit according to claim 10, wherein: neither of thethird and fourth materials is the same as the second material; and thefifth thermoelement is the same length as the fourth thermoelement. 12.A thermocouple probe comprising: a first thermocouple comprising firstand second thermoelements meeting at a first temperature measuringjunction, said first and second thermoelements being formed ofrespective first and second materials; a second thermocouple comprisingthird and fourth thermoelements meeting at a second temperaturemeasuring junction that is connected to the first thermoelement, saidthird and fourth thermoelements being formed of respective third andfourth materials, neither of said third and fourth materials being thesame as said first material; and a fifth thermoelement connected to saidsecond thermoelement and being formed of said fourth material; wherein:the fourth thermoelement is common to two voltage differencesubcircuits; and the third, fourth and fifth thermoelements areconnected to first, second and third electrical terminals, respectively,such that a first voltage difference is defined between the first andsecond electrical terminals, and a second voltage difference is definedbetween the second and third electrical terminals.
 13. The thermocoupleprobe according to claim 12, wherein: neither of the third and fourthmaterials is the same as the second material; and the fifththermoelement is the same length as the fourth thermoelement.
 14. Thethermocouple probe according to claim 12, further comprising: a matingassembly into which the first and second thermoelements are received,and from which the third, fourth and fifth thermoelements emerge. 15.The thermocouple probe according to claim 13, wherein the matingassembly comprises an electrically non-conductive plug through which thethird, fourth and fifth thermoelements pass, the second temperaturemeasuring junction being located on an upstream side of the plug. 16.The thermocouple probe according to claim 13, wherein the matingassembly comprises an electrically non-conductive plug through which thefirst and second thermoelements pass, the second temperature measuringjunction being located on a downstream side of the plug.
 17. Thethermocouple probe according to claim 13, wherein the mating assemblycomprises an electrically insulating potting material, said secondtemperature measuring junction being embedded in said electricallyinsulating potting material.
 18. The thermocouple probe according toclaim 16, comprising a pigtail assembly provided on a downstream side ofthe potting material.
 19. A thermocouple assembly comprising: athermocouple probe comprising: a first thermocouple comprising first andsecond thermoelements meeting at a first temperature measuring junction,said first and second thermoelements being formed of respective firstand second materials; a second thermocouple comprising third and fourththermoelements meeting at a second temperature measuring junction thatis connected to the first thermoelement, said third and fourththermoelements being formed of respective third and fourth materials,neither of said third and fourth materials being the same as said firstmaterial; and a fifth thermoelement connected to said secondthermoelement and being formed of said fourth material; and a cabledetachably connected to said third, fourth and fifth thermoelements ofsaid thermocouple probe, said cable comprising first and secondconductors formed of said fourth material and connected to said fourthand fifth thermoelements, and a third conductor formed of said thirdmaterial and connected to said third thermoelement; wherein: the third,fourth and fifth thermoelements are connected to first, second and thirdelectrical terminals, respectively, such that a first voltage differenceis defined between the first and second electrical terminals, and asecond voltage difference is defined between the second and thirdelectrical terminals.
 20. The multi-element thermocouple circuitaccording to claim 19, wherein: neither of the third and fourthmaterials is the same as the second material; and the fifththermoelement is the same length as the fourth thermoelement.
 21. Thethermocouple assembly according to claim 19, wherein the fourththermoelement is common to two voltage difference subcircuits.
 22. Amethod of measuring a temperature at a first temperature measuringjunction, comprising: providing a thermocouple probe comprising: a firstthermocouple comprising first and second thermoelements meeting at afirst temperature measuring junction, said first and secondthermoelements being formed of respective first and second materials; asecond thermocouple comprising third and fourth thermoelements meetingat a second temperature measuring junction that is connected to thefirst thermoelement, said third and fourth thermoelements being formedof respective third and fourth materials, neither of said third andfourth materials being the same as said first material; and a fifththermoelement connected to said second thermoelement and being formed ofsaid fourth material; wherein: the fourth thermoelement is common to twovoltage difference subcircuits; measuring a first voltage differencebetween the third and fourth thermoelements; measuring a second voltagedifference between the fourth and fifth thermoelements; and determiningthe temperature at the first temperature measuring junction based atleast in part on the first and second voltage differences.
 23. Amulti-element thermocouple circuit comprising: a first thermocouplecomprising first and second thermoelements meeting at a firsttemperature measuring junction and having respective first and seconddistal ends, said first and second thermoelements being formed ofrespective first and second materials; a second thermocouple comprisingthird and fourth thermoelements meeting at a second temperaturemeasuring junction that is connected to said first distal end, saidthird and fourth thermoelements having respective third and fourthdistal ends and being formed of respective third and fourth materials,neither of said third and fourth materials being the same as said firstmaterial; and a fifth thermoelement having a fifth proximal endconnected to said second distal end and a fifth distal end, the fifththermoelement being formed of said fourth material; wherein: the fourththermoelement is common to two voltage difference subcircuits; and thedistal ends of the third, fourth and fifth thermoelements aresufficiently electrically isolated from one another such that, whenmeasuring a temperature at the first temperature measuring junction, afirst open circuit voltage appears across distal ends of the third andfourth thermoelements and a second open circuit voltage appears acrossdistal ends of the fourth and fifth thermoelements.